8.1 What programs does Debian provide for managing its packages?

There are multiple tools that are used to manage Debian packages, from graphic
or text-based interfaces to the low level tools used to install packages. All
the available tools rely on the lower level tools to properly work and are
presented here in decreasing complexity level.

It is important to understand that the higher level package management tools
such as aptitude or dselect rely on apt
which, itself, relies on dpkg to manage the packages in the
system.

8.1.1 dpkg

This is the main package management program. dpkg can be invoked
with many options. Some common uses are:

Find out all the options: dpkg --help.

Print out the control file (and other information) for a specified package:
dpkg --info foo_VVV-RRR.deb

Install a package (including unpacking and configuring) onto the file system of
the hard disk: dpkg --install foo_VVV-RRR.deb.

Unpack (but do not configure) a Debian archive into the file system of the hard
disk: dpkg --unpack foo_VVV-RRR.deb. Note that this operation
does not necessarily leave the package in a usable state; some files
may need further customization to run properly. This command removes any
already-installed version of the program and runs the preinst (see What is a Debian preinst, postinst,
prerm, and postrm script?, Section 7.6) script associated with the package.

Configure a package that already has been unpacked: dpkg --configure
foo. Among other things, this action runs the postinst (see What is a Debian preinst, postinst,
prerm, and postrm script?, Section 7.6) script associated with the package.
It also updates the files listed in the conffiles for this
package. Notice that the 'configure' operation takes as its argument a package
name (e.g., foo), not the name of a Debian archive file (e.g.,
foo_VVV-RRR.deb).

Extract a single file named "blurf" (or a group of files named
"blurf*" from a Debian archive: dpkg --fsys-tarfile
foo_VVV-RRR.deb | tar -xf - blurf*

8.1.2 APT

APT is the Advanced Package Tool and provides the apt-get
program. apt-get provides a simple way to retrieve and install
packages from multiple sources using the command line. Unlike
dpkg, apt-get does not understand .deb files, it
works with the packages proper name and can only install .deb archives from a
source specified in /etc/apt/sources.list. apt-get
will call dpkg directly after downloading the .deb archives[5] from the configured sources.

Some common ways to use apt-get are:

To update the list of package known by your system, you can run:

apt-get update

(you should execute this regularly to update your package lists)

To upgrade all the packages on your system (without installing extra packages
or removing packages), run:

apt-get upgrade

To install the foo package and all its dependencies, run:

apt-get install foo

To remove the foo package from your system, run:

apt-get remove foo

To remove the foo package and its configuration files from your system, run:

apt-get --purge remove foo

To upgrade all the packages on your system, and, if needed for a package
upgrade, installing extra packages or removing packages, run:

apt-get dist-upgrade

(The command upgrade keeps a package at its installed obsolete
version if upgrading would need an extra package to be installed, for a new
dependency to be satisfied. The dist-upgrade command is less
conservative.)

Note that you must be logged in as root to perform any commands that modify the
system packages.

Note that apt-get now installs recommended packages as default and
is the preferred program for package management from console to perform system
installation and major system upgrades for its robustness.

The apt tool suite also includes the apt-cache tool to query the
package lists. You can use it to find packages providing specific
functionality through simple text or regular expression queries and through
queries of dependencies in the package management system. Some common ways to
use apt-cache are:

To find packages whose description contain word:

apt-cache search word

To print the detailed information of a package:

apt-cache show package

To print the packages a given package depends on:

apt-cache depends package

To print detailed information of the versions available for a package and the
packages that reverse-depends on it:

apt-cache showpkg package

For more information, install the apt package and read
apt-get(8), sources.list(5) and install the
apt-doc package and read
/usr/share/doc/apt-doc/guide.html/index.html.

8.1.3 aptitude

aptitude is a package manager for Debian GNU/Linux systems that
provides a frontend to the apt package management infrastructure.
aptitude is a text-based interface using the curses library, it
can be used to perform management tasks in a fast and easy way.

aptitude provides the functionality of dselect and
apt-get, as well as many additional features not found in either
program:

aptitude offers easy access to all versions of a package.

aptitude makes it easy to keep track of obsolete software by
listing it under "Obsolete and Locally Created Packages".

aptitude includes a fairly powerful system for searching
particular packages and limiting the package display. Users familiar with
mutt will pick up quickly, as mutt was the
inspiration for the expression syntax.

aptitude can be used to install the predefined tasks available.
For more information see tasksel, Section 8.1.5.

aptitude in full screen mode has su functionality
embedded and can be run by a normal user. It will call su (and
ask for the root password, if any) when you really need administrative
privileges

You can use aptitude through a visual interface (simply run
aptitude) or directly from the command line. The command line
syntax used is very similar to the one used in apt-get. For
example, to install the foo package, you can run aptitude
install foo.

Note that aptitude is the preferred program for daily package
management from console.

For more informations, read the manual page aptitude(8) and
install the aptitude-doc package.

8.1.4 synaptic

synaptic is a graphical package manager. It enables you to
install, upgrade and remove software packages in a user friendly way. Next to
all features offered by aptitude, it also has a feature for editing the list of
used repositories, and supports browsing all available documentation related to
a package. See the Synaptic
Website for more information.

8.1.5 tasksel

When you want to perform a specific task it might be difficult to find the
appropiate suite of packages that fill your need. The Debian developers have
defined tasks, a task is a collection of several individual Debian
packages all related to a specific activity. Tasks can be installed through
the tasksel program or through aptitude.

The Debian installer will typically install automaticaly the task associated
with a standard system and a desktop environment. The specific desktop
environment installed will depend on the CD/DVD media used, most commonly it
will be the GNOME desktop (gnome-desktop task). Also, depending
on your selections throughout the installation process, tasks might be
automatically installed in your system. For example, if you selected a
language, the task associated with it will be installed automatically too and
if you are running in a laptop system the installer recognises the
laptop task will be installed too.

8.1.6 Other package management tools

8.1.6.1 dselect

This program is a menu-driven interface to the Debian package management
system. For woody and earlier releases, this was the main package management
interface for for first-time installations, but currently users are encouraged
to use aptitude instead. Some users might feel more comfortable
using aptitude and it is also recommended over
dselect for large-scale upgrades. For more information on
aptitude please see aptitude, Section
8.1.3.

dselect can:

guide the user as he/she chooses among packages to install or remove, ensuring
that no packages are installed that conflict with one another, and that all
packages required to make each package work properly are installed;

warn the user about inconsistencies or incompatibilities in their selections;

determine the order in which the packages must be installed;

automatically perform the installation or removal; and

guide the user through whatever configuration process are required for each
package.

dselect begins by presenting the user with a menu of 7 items, each
of which is a specific action. The user can select one of the actions by using
the arrow keys to move the highlighter bar, then pressing the
<enter> key to select the highlighted action.

What the user sees next depends on the action he selected. If he selects any
option but Access or Select, then
dselect will simply proceed to execute the specified action: e.g.,
if the user selected the action Remove, then dselect would proceed
to remove all of the files selected for removal when the user last chose the
Select action.

Both the Access menu item and the Select menu item
lead to additional menus. In both cases, the menus are presented as split
screens; the top screen gives a scrollable list of choices, while the bottom
screen gives a brief explanation ("info") for each choice.

Extensive on-line help is available, use the '?' key to get to a help screen
at any time.

The order in which the actions are presented in the first dselect
menu represents the order in which a user would normally choose
dselect to install packages. However, a user can pick any of the
main menu choices as often as needed (including not at all, depending on what
one wants to do).

Begin by choosing an Access Method. This is the method by
which the user plans on accessing Debian packages; e.g., some users have Debian
packages available on CD-ROM, while others plan to fetch them using anonymous
FTP. The selected "Access Method" is stored after
dselect exits, so if it does not change, then this option need not
be invoked again.

Then Update the list of available packages. To do this,
dselect reads the file "Packages.gz" which should be
included in the top level of the directory where the Debian packages to be
installed are stored. (But if it is not there, dselect will offer
to make it for you.)

Select specific packages for installation on his system.
After choosing this menu item, the user is first presented with a full screen
of help (unless the `--expert' command line option was used). Once the user
exits the Help screen, he sees the split-screen menu for choosing packages to
install (or remove).

The top part of the screen is a relatively narrow window into the list of
Debian's 29000 packages; the bottom part of the screen contains description of
the package or group of packages which are highlighted above.

One can specify which packages should be operated on by highlighting a package
name or the label for a group of packages. After that, you can select
packages:

to be installed:

This is accomplished by pressing the `+' key.

to be deleted:

Packages can be deleted two ways:

removed: this removes most of the files associated with the package, but
preserves the files listed as configuration files (see What is a Debian conffile?, Section
7.5) and package configuration information. This is done by pressing the
`-' key.

purged: this removes every file that is part of the package. This is
done by pressing the `_' key.

Note that it's not possible to remove "All Packages". If you try
that, your system will instead be reduced to the initial installed base
packages.

to be put "on hold"

This is done by pressing `=', and it effectively tells dselect not
to upgrade a package even if the version currently installed on your system is
not as recent as the version that is available in the Debian repository you are
using (this was specified when you set the Access Method, and
acquired when you used Update).

Just like you can put a package on hold, you can reverse such setting by
pressing `:'. That tells dselect that the package(s) may be
upgraded if a newer version is available. This is the default setting.

You can select a different order in which the packages are presented, by using
the `o' key to cycle between various options for sorting the packages. The
default order is to present packages by Priority; within each priority,
packages are presented in order of the directory (a.k.a. section) of the
archive in which they are stored. Given this sort order, some packages in
section A (say) may be presented first, followed by some packages in section B,
followed by more packages (of lower priority) in section A.

You can also expand meanings of the labels at the top of the screen, by using
the `v' (verbose) key. This action pushes much of the text that formerly fit
onto the display off to the right. To see it, press the right arrow; to scroll
back to the left, press the left arrow.

If you select a package for installation or removal, e.g.,
foo.deb, and that package depends on (or recommends) another
package, e.g., blurf.deb, then dselect will place the
you in a sub-screen of the main selection screen. There you can choose among
the related packages, accepting the suggested actions (to install or not), or
rejecting them. To do the latter, press Shift-D; to return to the former,
press Shift-U. In any case, you can save your selections and return to the
main selection screen by pressing Shift-Q.

Users returning to the main menu can then select the "Install" menu
item to unpack and configure the selected packages. Alternatively, users
wishing to remove files can choose the "Remove" menu item. At any
point, users can choose "Quit" to exit dselect; users' selections are
preserved by dselect.

8.1.6.2 dpkg-deb

This program manipulates Debian archive(.deb) files. Some common
uses are:

Find out all the options: dpkg-deb --help.

Determine what files are contained in a Debian archive file: dpkg-deb
--contents foo_VVV-RRR.deb)

Extract the files contained in a named Debian archive into a user specified
directory: dpkg-deb --extract foo_VVV-RRR.deb tmp extracts each of
the files in foo_VVV-RRR.deb into the directory tmp/.
This is convenient for examining the contents of a package in a localized
directory, without installing the package into the root file system.

Extract the control information files from a package: dpkg-deb --control
foo_VVV-RRR.deb tmp.

Note that any packages that were merely unpacked using dpkg-deb
--extract will be incorrectly installed, you should use dpkg
--install instead.

More information is given in the manual page dpkg-deb(1).

8.1.6.3 dpkg-split

This program splits large package into smaller files (e.g., for writing onto a
set of floppy disks), and can also be used to merge a set of split files back
into a single file. It can only be used on a Debian system (i.e. a system
containing the dpkg package), since it calls the program
dpkg-deb to parse the debian package file into its component
records.

For example, to split a big .deb file into N parts,

Execute the command dpkg-split --split foo.deb. This will produce
N files each of approximately 460 KBytes long in the current directory.

Copy those N files to floppy disks.

Copy the contents of the floppy disks onto the hard disk of your choice on the
other machine.

Join those part-files together using dpkg-split --join
"foo*".

8.2 Debian claims to be able to update a running program; how is this accomplished?

The kernel (file system) in Debian GNU/Linux systems supports replacing files
even while they're being used.

We also provide a program called start-stop-daemon which is used
to start daemons at boot time or to stop daemons when the runlevel is changed
(e.g., from multi-user to single-user or to halt). The same program is used by
installation scripts when a new package containing a daemon is installed, to
stop running daemons, and restart them as necessary.

8.3 How can I tell what packages are already installed on a Debian system?

To learn the status of all the packages installed on a Debian system, execute
the command

dpkg --list

This prints out a one-line summary for each package, giving a 2-letter status
symbol (explained in the header), the package name, the version which is
installed, and a brief description.

To learn the status of packages whose names match the string any pattern
beginning with "foo" by executing the command:

dpkg --list 'foo*'

To get a more verbose report for a particular package, execute the command:

dpkg --status packagename

8.4 How to display the files of a package installed?

To list all the files provided by the installed package foo
execute the command

dpkg --listfiles foo

Note that the files created by the installation scripts aren't displayed.

8.5 How can I find out what package produced a particular file?

To identify the package that produced the file named foo execute
either:

dpkg --search filename

This searches for filename in installed packages. (This is
(currently) equivalent to searching all of the files having the file extension
of .list in the directory /var/lib/dpkg/info/, and
adjusting the output to print the names of all the packages containing it, and
diversions.)

A faster alternative to this is the dlocate tool.

dlocate -S filename

zgrep foo Contents-ARCH.gz

This searches for files which contain the substring foo in their
full path names. The files Contents-ARCH.gz (where ARCH
represents the wanted architecture) reside in the major package directories
(main, non-free, contrib) at a Debian FTP site (i.e. under
/debian/dists/squeeze). A Contents file refers only
to the packages in the subdirectory tree where it resides. Therefore, a user
might have to search more than one Contents files to find the
package containing the file foo.

This method has the advantage over dpkg --search in that it will
find files in packages that are not currently installed on your system.

apt-file search foo

If you install the apt-file, similar to the above, it searches
files which contain the substring or regular expression foo in
their full path names. The advantage over the sample above is that there is no
need to retrieve the Contents-ARCH.gz files as it will do this
automatically for all the sources defined in /etc/apt/sources.list
when you run (as root) apt-file update.

8.6 Why doesn't get `foo-data' removed when I uninstall `foo'? How do I make sure old unused library-packages get purged?

Some packages are split in program (`foo') and data (`foo-data') (or in `foo'
and `foo-doc'). This is true for many games, multimedia applications and
dictionaries in Debian and has been introduced since some users might want to
access the raw data without installing the program or because the program can
be run without the data itself, making it optional.

Similar situations occur when dealing with libraries: generally these get
installed since packages containing applications depend on them. When the
application-package is purged, the library-package might stay on the system.
Or: when the application-package no longer depends upon e.g. libdb4.2, but
upon libdb4.3, the libdb4.2 package might stay when the application-package is
upgraded.

In these cases, `foo-data' doesn't depend on `foo', so when you remove the
`foo' package it will not get automatically removed by most package management
tools. The same holds true for the library packages. This is necessary to
avoid circular dependencies. If you use aptitude (see aptitude, Section 8.1.3) as your package management tool
it will, however, track automatically installed packages and remove them when
no packages remain that need them in your system.